1. Field of the Invention
The present invention relates to a thin film magnetic head and, more particularly, to a horizontal thin film magnetic head of a composite construction comprising a magnetoresistance-effect magnetic head (hereinafter referred to as "MR magnetic head") employing a magnetoresistance-effect element (hereinafter referred to as "MR element") and an inductive recording head.
2. Description of the Prior Art
A horizontal thin film magnetic head has become an object of attention owing to its advantages in dealing with narrow tracks with the recent progressive increase in magnetic recording density. On the other hand, many studies of MR magnetic head employing a MR element advantageous in respect of reproducing sensitivity have been made, and a horizontal MR thin film magnetic head comprising, in combination, a horizontal thin film magnetic head and a MR magnetic head has been proposed.
Such a horizontal MR thin film magnetic head is proposed, for example, in Japanese Patent Laid-open (Kokai) No. Sho 62-134814 for the applicant of the present patent application. As shown in a schematic enlarged sectional view in FIG. 9, this previously proposed horizontal MR thin film magnetic head has a MR magnetic head having a magnetic circuit forming a closed magnetic path, comprising a pair of magnetic cores 38A and 38B disposed opposite to each other with a magnetic head gap g formed between the opposite ends thereof facing a magnetic recording medium, a magnetoresistance-effect element (hereinafter referred to as "MR element") 13 having opposite ends magnetically connected to the magnetic cores 38A and 38B, and a bias conductor layer 16 surrounded by the magnetic cores 38A and 38B and the MR element 13 and embedded in an insulating layer 8. The bias conductor layer 16 is extended perpendicularly to the longitudinal direction of the MR element 13. Portions of the pair of magnetic cores 38A and 38B, and the surface of a protective layer 39 form an air bearing surface 30.
As shown in a schematic enlarged sectional view in FIG. 10, the MR element 13 has a two-layer construction comprising a 300 .ANG. thick MR thin film MR.sub.A formed of NiFe, a 300 .ANG. thick MR thin film MR.sub.B, and a nonmagnetic layer 35 formed of Al.sub.2 O.sub.3, having a thickness that allows the magnetostatic coupling of the MR thin films MR.sub.A and MR.sub.B and does not allow the mutual interaction of the MR thin films MR.sub.A and MR.sub.B, for example, 60 .ANG., and sandwiched between the MR thin films MR.sub.A and MR.sub.B. The axes of easy direction of magnetization of the MR thin films MR.sub.A and MR.sub.B are extended along the width of the MR thin films MR.sub.A and MR.sub.B. When sense currents I.sub.s are supplied to the MR thin films MR.sub.A and MR.sub.B along the axes of difficult direction of magnetization, the growth of magnetic domain walls is suppressed and Barkhausen noise can be reduced.
When the closed magnetic path is thus formed by providing the MR element 13 in the magnetic path provided with the magnetic head gap g, the length of the magnetic path between the magnetic head gap g and the MR element 13 is small, which improves the reproducing efficiency. Furthermore, the horizontal construction enables providing a high output voltage and a large S/N ratio. Since the MR element 13 is spaced apart a sufficiently large distance from the air bearing surface 30, the horizontal MR thin film magnetic head can be processed stably and has stable reliability. However, the construction of a recording head is not taken into construction in designing the horizontal MR thin film magnetic head.
The applicant of the present patent application proposed previously a thin film magnetic head in Japanese Patent Application No. Hei 1-253673. As shown in FIG. 11, this previously proposed thin film magnetic head has a front core 42 provided with a magnetic head gap g and extended in parallel to an air bearing surface 30, a MR element 13 of a laminate construction consisting of magnetostatically coupled MR thin films and a nonmagnetic film sandwiched between the MR thin films, formed so as to extend across the magnetic head gap g on the front core 42, a bias conductor layer 45 formed over the MR element 13 to apply a bias magnetic field to the same, an insulating layer 46 enclosing the MR element 13 and the bias conductor layer 45, a head coil 47 formed on the insulating layer 46, an insulating layer 48 covering the head coil 47, and a back core 42 extending over part of the head coil 47 and having opposite ends joined respectively to the opposite ends of the front core 42.
Although the MR element 13 is disposed near the magnetic head gap g, in some cases, the back core 49 affect adversely to the reproducing efficiency.